biology : class11 Xylem Sap Composition : Mechanism, Guttation, Importance : Root Pressure MCQ Questions and Answers
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Xylem Sap Composition
MCQ questions and answers.
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MCQ Questions
1. Which description most accurately characterizes the composition of xylem sap in a normally transpiring plant?
A.
A dilute aqueous solution containing mainly inorganic ions, with smaller amounts of organic solutes and dissolved gases
B.
A concentrated solution composed almost entirely of sucrose transported from leaves
C.
A suspension of living xylem cells rich in proteins and starch granules
D.
A lipid-rich emulsion containing predominantly phospholipids and triglycerides
Correct Answer:
A dilute aqueous solution containing mainly inorganic ions, with smaller amounts of organic solutes and dissolved gases
Explanation:
Xylem sap is primarily water containing absorbed mineral ions. It may also contain small quantities of amino acids, organic acids, hormones, and dissolved gases, but it is not mainly composed of sugars, cells, or lipids.
2. Which set contains substances that can all occur as solutes in xylem sap?
A.
Nitrate ions, potassium ions, amino acids, and organic acids
B.
Starch granules, cellulose fibres, triglycerides, and intact chloroplasts
C.
Large ribosomal subunits, chromosomal DNA, glycogen granules, and waxes
D.
Cellulose microfibrils, cutin polymers, phospholipid bilayers, and lignin crystals
Explanation:
Xylem sap can contain inorganic mineral ions such as nitrate and potassium, together with low concentrations of organic solutes such as amino acids and organic acids. The other groups consist mainly of insoluble structural materials or cellular components.
3. A chemical analysis of xylem sap shows a high concentration of nitrate ions and a lower concentration of amino acids. Which interpretation is most appropriate?
A.
The sap contains both mineral nutrients and transported organic nitrogenous compounds
B.
The sap must be phloem sap because nitrate cannot occur in xylem
C.
The amino acids prove that xylem vessels are living cells that synthesize proteins
D.
The nitrate ions must have originated from the breakdown of cellulose in vessel walls
Correct Answer:
The sap contains both mineral nutrients and transported organic nitrogenous compounds
Explanation:
Xylem sap commonly carries inorganic nitrogen mainly as nitrate or other mineral forms and may also contain organic nitrogenous compounds such as amino acids. Their presence does not mean that xylem vessels themselves are living or that nitrate comes from cellulose.
4. Why is the concentration of mineral ions in xylem sap not necessarily identical to the concentration in the soil solution surrounding the roots?
A.
Root cells selectively absorb and release ions before they enter the xylem
B.
Xylem vessels chemically convert every absorbed ion into sucrose
C.
Soil water enters xylem without crossing any living root tissue
D.
Mineral ions are excluded from xylem sap unless they are bound to proteins
Correct Answer:
Root cells selectively absorb and release ions before they enter the xylem
Explanation:
The ionic composition of xylem sap is modified by selective uptake, transport, storage, and loading processes in root tissues. Consequently, xylem sap composition can differ substantially from that of the external soil solution.
5. Which observation would most strongly support the conclusion that a collected sample is xylem sap rather than pure water?
A.
It contains measurable potassium, nitrate, calcium, and magnesium ions
B.
It is transparent and has no visible suspended particles
C.
It freezes at a temperature close to that of pure water
D.
It has no detectable colour when viewed in a glass tube
Correct Answer:
It contains measurable potassium, nitrate, calcium, and magnesium ions
Explanation:
The characteristic chemical evidence for xylem sap is the presence of dissolved mineral nutrients. Transparency, lack of visible particles, and near-normal freezing behaviour do not distinguish it reliably from pure water.
6. Which statement best explains why xylem sap can contain organic acids even though xylem transport is mainly associated with mineral nutrition?
A.
Organic acids may be transported as metabolic products or may participate in ionic balance and mineral transport
B.
Organic acids are produced only by dead xylem vessels after the sap leaves the root
C.
Organic acids replace water as the principal solvent in the xylem
D.
Organic acids are structural polymers that form the walls of xylem vessels
Correct Answer:
Organic acids may be transported as metabolic products or may participate in ionic balance and mineral transport
Explanation:
Although xylem sap is dominated by water and inorganic ions, it can contain organic acids. These compounds may arise from metabolism and can contribute to charge balance or complexation and transport of mineral ions.
7. A xylem-sap sample contains water, inorganic ions, small quantities of amino acids, and trace plant hormones. Which conclusion is most justified?
A.
Xylem sap can transport both mineral nutrients and certain signalling or organic compounds
B.
The sample must be phloem sap because hormones cannot occur in xylem
C.
The sample is not xylem sap because xylem carries only water and no solutes
D.
The amino acids must have been formed from lignin during upward movement
Correct Answer:
Xylem sap can transport both mineral nutrients and certain signalling or organic compounds
Explanation:
Xylem sap is not pure water. Along with mineral ions, it may carry small amounts of organic compounds, including amino acids and certain plant hormones, allowing chemical signals and nutrients to move through the plant.
8. Which change would most directly increase the osmotic concentration of xylem sap, assuming the volume of water remains constant?
A.
An increase in dissolved nitrate and potassium ions
B.
An increase in the diameter of xylem vessels without adding solutes
C.
Removal of dissolved ions while retaining the same amount of water
D.
Conversion of dissolved ions into insoluble deposits within vessel walls
Correct Answer:
An increase in dissolved nitrate and potassium ions
Explanation:
Osmotic concentration depends on the number of dissolved particles. Adding nitrate and potassium ions increases the solute concentration of xylem sap when the water volume remains unchanged.
9. Which statement correctly distinguishes the major solute pattern of xylem sap from that of phloem sap?
A.
Xylem sap generally contains abundant inorganic ions, whereas phloem sap commonly contains much more transported sucrose
B.
Xylem sap contains only proteins, whereas phloem sap contains only mineral ions
C.
Both saps have identical compositions because they move through vascular tissue
D.
Xylem sap is lipid-based, whereas phloem sap is composed mainly of cellulose fibres
Correct Answer:
Xylem sap generally contains abundant inorganic ions, whereas phloem sap commonly contains much more transported sucrose
Explanation:
Xylem sap is primarily water with mineral ions and smaller amounts of organic substances. Phloem sap is characteristically rich in transported organic solutes, especially sucrose, so their dominant solute patterns differ.
10. If a plant is supplied with a nutrient solution containing nitrate, potassium, calcium, and sulfate ions, which result would be most consistent with xylem sap composition after root uptake?
A.
The xylem sap contains these ions in proportions modified by selective root transport
B.
The xylem sap must contain the ions in exactly the same proportions as the nutrient solution
C.
Only nitrate can enter the xylem because other ions are excluded from vascular tissue
D.
The ions disappear from the sap because xylem transports only uncharged molecules
Correct Answer:
The xylem sap contains these ions in proportions modified by selective root transport
Explanation:
All four listed ions can be transported in xylem sap, but roots regulate their uptake and loading. Therefore, the final xylem composition need not reproduce the proportions present in the external nutrient solution.
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